1. Field of the Invention
The present invention relates to television receivers and, more particularly, to a television receiver which can receive a satellite television broadcasting and a VHF (very high frequency) and UHF (ultra high frequency) television broadcasting simultaneously.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings shows an example of a previously-proposed television receiver which can simultaneously receive a satellite television broadcasting and a VHF and UHF television broadcasting.
In FIG. 1, reference numeral 1 depicts a VHF and UHF television broadcasting receiving apparatus which includes VHF and UHF tuners, an intermediate frequency amplifying circuit, a detector circuit or the like, though not shown. A video signal of VHF or UHF television broadcasting developed at the output side of the VHF and UHF television broadcasting receiving apparatus 1 is supplied to one fixed contacts 2b and 3b of change-over switches 2 and 3.
In FIG. 1, reference numeral 4 depicts a satellite television broadcasting receiving apparatus which includes satellite television broadcasting receiving converter, a tuner, an intermediate frequency amplifying circuit, a detector circuit or the like, though not shown. A video signal of the satellite television broadcasting developed at the output side of the satellite television broadcasting receiving apparatus 4 is supplied to the other fixed contacts 2c and 3c of the change-over switches 2 and 3. A video signal developed at a movable contact 2a of the change-over switch 2 is supplied to a video signal processor circuit 5 and synchronizing and deflecting circuit 6, both of which construct an image display unit. An output signal from the video signal processor circuit 5 is supplied to a cathode ray tube (CRT) 7, and a deflection or the like is performed by using an output signal from the synchronizing and deflecting circuit 6. Then, a picture of this video signal is displayed on the cathode ray tube 7.
The video signal developed at a movable contact 3a of the change-over switch 3 is supplied to an external output unit 8, such as a pin jack or the like that supplies a video signal to a video tape recorder, an external monitor display or the like.
In the television receiver shown in FIG. 1, by connecting the movable contact 2a of the change-over switch 2 to one and the other fixed contacts 2b and 2c, pictures of the VHF and UHF television broadcastings and the satellite television broadcasting can be selectively displayed on the cathode ray tube 7 so that the viewer can watch a desired television broadcasting.
Further, by selectively connecting the movable contact 3a of the change-over switch 3 to one and the other fixed contacts 3b and 3c, the video signals of the VHF and UHF television broadcastings and the video signal of the satellite broadcasting are selectively supplied to the external output unit 8 to which the video tape recorder or the like is connected. Therefore, the viewer can record a video signal of a desired television broadcasting.
Furthermore, in the television receiver shown in FIG. 1, the video signal of the satellite television broadcasting or the VHF and UHF television broadcasting can be simultaneously recorded via the external output unit 8 while a picture of a video signal of the VHF and UHF television broadcasting or satellite television broadcasting is being received and reproduced on the cathode ray tube 7.
The conventional television receiver shown in FIG. 1, however, suffers from the following disadvantage. That is, if a broadcasting of a desired station of the VHF and UHF television broadcasting is finished and no video signal is received while the video signal of a desired station of the satellite television broadcasting is recorded by the video tape recorder (not shown) connected to the external output unit 8 and a video signal of a desired station of the VHF and UHF television broadcasting is received by the cathode ray tube 7, then an oscillator in the synchronizing and detecting circuit 6 of the video display unit is freely oscillated and a noise signal caused by this free oscillation of the oscillator is mixed into the video signal of the external output unit 8. Consequently, the video signal from the external output unit 8 is disturbed by this noise signal.